1. Field of the Invention
The present invention relates to a rotation control device of working machine for rotating and driving a rotating body by an electric motor.
2. Description of the Related Art
In a rotation working machine such as an excavator and a crane, a hydraulic motor driven by discharge oil of a hydraulic pump serves as a driving source of a rotating body. However, in recent years, there is a known technique that the driving source is an electric motor (for example, Japanese Patent Laid-Open No. 2001-10783, hereinafter referred to as Patent Document 1).
In such a case, due to speed control for determining a torque instruction with using a deviation between target speed set in accordance with an operation amount of a rotation operating lever and actual rotation speed (what is called speed feedback control), when the above deviation is increased, acceleration torque is radically increased and shock is generated.
Meanwhile, there is a known technique that while PID control is performed, torque restriction is added in accordance with the operation amount as in Japanese Patent Laid-Open No. 2004-36303 (hereinafter, referred to as Patent Document 2), and there is another known technique that with using a jerk probable value calculated by second-order differential of the target speed, the target speed is corrected as in Japanese Patent Laid-Open No. 2004-137702 (hereinafter, referred to as Patent Document 3).
Further, in order to prevent the generation of the shock, there is a known technique that a dynamic characteristic of the electric motor imitates a drive characteristic of a hydraulic motor as in Japanese Patent Laid-Open No. 2003-333876 (hereinafter, referred to Patent Document 4).
However, the techniques of Patent Documents 2 to 4 are to control rotating and driving on the basis of only the operation amount of the rotation lever, and therefore not capable of suppressing effectively the generation of the shock in an actual machine.
That is, in the actual working machine, even when the operation amount of the lever is constant, necessary torque for rotating a rotating body is changed in accordance with a working state thereof (such as a working state of a working attachment and an inclination angle of the working machine itself). Therefore, the working machine has a characteristic that the speed deviation is radically changed in accordance with an amount of the torque.
Therefore, in the techniques according to Patent Documents 2 to 4, with a large amount of the necessary torque, the speed deviation is increased despite of a small operation amount of the lever by an operator, and as a result, there is a fear that the torque given to the electric motor is increased so as to generate the shock.
In the speed feedback control, in order to improve a following property to the speed, in the case of the PID control for example, gain is increased to as a large amount as possible. However, in the case where the gain is increased, the deviation between the target speed and the actual rotation speed is small but instruction torque to the electric motor is excessively increased by a small amount of the lever operation. Therefore, in the case where a rotation pressing work by a bucket is performed, there is sometimes a case where adjustment of the pressing force is difficult. Further, in the case where a radical lever operation is performed, there is sometimes a case where the instruction torque to the electric motor is radically increased so as to generate the shock.
Conversely, in order to facilitate the adjustment of the instruction torque to the electric motor by the lever operation, in the case of the PID control for example, there is sometimes a case where the gain is decreased or integral gain is made to be zero. However, in the case where the gain is decreased, in a working state in an inclined ground (a state of receiving weight of the working machine itself) and the like, the instruction torque to the electric motor is excessively decreased so that it is not possible to ensure sufficient acceleration/deceleration torque and spot-maintenance torque.
As a technique for solving the problem of the speed feedback control, there are known techniques disclosed in Patent Documents 2, 5 to 7. The techniques are to properly switch between the two control systems mentioned above.
Specifically, Patent Document 5 (Japanese Patent Laid-Open No. 2003-328398) discloses a technique of switching between the speed feedback control and torque control taking a fixed operation amount of the operating lever as a border. Patent Document 6 (International Publication No. 2005/111322) discloses a technique of switching between speed control and position control taking a speed threshold value of the target speed in accordance with the operation amount of the lever as a border. Patent Document 7 (Japanese Patent Laid-Open No. 2005-273262) discloses a technique of switching between normal speed control and speed control with proportional gain which is more decreased than the above speed control taking predetermined speed of the rotating body as a border.
Patent Document 2 discloses a technique of performing position maintenance control when the operation amount of the operating lever is in a neutral range which is preliminarily set, while performing the torque control when the operation amount exceeds the neutral range.
However, in the case where the two control systems are switched as in Patent Documents mentioned above, at a point of switching between the control systems, the torque is discontinuously changed (radically changed) in order to fill a gap between the control systems so that it is not possible to smoothly and stably perform the control.
In the technique of Patent Document 2, in a state after the operation amount of the lever exceeds the neutral range, rotating and driving are performed with larger torque among the spot-maintenance torque and the acceleration torque. However, the spot-maintenance torque is torque which is generated in the position maintenance control executed within the neutral range and hence required in the past, and therefore not torque which reflects the working state at the present. Therefore, when the torque for maintaining the rotating body on the spot is larger at the time of executing the torque control than at the time of executing the position maintenance control, there is a fear that the rotating body is adversely moved against intention of the operator.